1. Field of the Invention
The invention relates to unsaturated fatty alcohols which are obtained by fractionating palm oil fatty acid methyl esters, and then hydrogenating the fraction of unsaturated long-chain methyl esters, and to a process for the preparation of these fatty alcohols.
2. Statement of Related Art
Unsaturated fatty alcohols are important intermediates for a large number of products of the chemical industry, such as, for example, for the preparation of surfactants and skincare products. A review on this topic can be found, for example, by U. Ploog et al. in Seifen-Öle-Fette-Wachse [Soaps-Oils-Fats-Waxes] 109, 225 (1983). They are prepared from more or less unsaturated fatty acid methyl esters which can be hydrogenated, for example, in the presence of chromium- or zinc-containing mixed catalysts [Ullmann's Encyclopedia of Industrial Chemistry, Verlag Chemie, Weinheim, 4th Edition, Vol. 11, p. 436 ff]. The prior art is a large-scale process, as has hitherto also been carried out by the applicant, according to which animal fats and oils are used, and the unsaturated fatty alcohols produced after the hydrogenation are distilled at a still temperature of e.g. 220 to 250° C. and a reduced pressure of from 1 to 20 mbar—measured at the top of the column. Since the preparation of unsaturated fatty alcohols is associated with high costs, distillation has been carried out with as low a raw material loss as possible. In fact, in this way, it was possible to achieve a yield of about 90% of theory, and correspondingly a loss of 10%, although the products exhibited a marked intrinsic odor. A further disadvantage is that the fatty alcohols of the prior art have unsatisfactory storage and low-temperature behavior.
For application reasons, unsaturated fatty alcohols having iodine numbers of from 50 to 80 are particularly preferred since these have a solidification point which is favorable for use in cosmetic products. Unsaturated fatty alcohols having iodine numbers in the abovementioned range are currently largely based on animal raw materials. The desired iodine number range is set by blending different products having differing iodine number ranges. Adjustment of the iodine number range by distillative methods is not possible since the iodine number or iodine number range of animal-based fatty acids or fatty alcohols remains virtually constant during fractionation. However, animal fats have the disadvantage that they have a very heterogeneous structure. For example, animal fats contain nitrogen-containing compounds, such as amides or steroids, such as, for example, cholesterol, which are directly or indirectly responsible for the abovementioned unpleasant odor of the products. The nitrogen-containing compounds can become involved in secondary reactions, which impairs product stability, in particular oxidation stability, and leads to discolored products. In addition, because of the continuing BSE debate, products which are prepared using beef tallow are viewed extremely critically by the consumer. In the cosmetics market, there is therefore a continuous need for ever purer raw materials of ever higher quality, a demand which can usually only be met by ever more complex industrial processes and additional purification steps. In the case of unsaturated fatty alcohols, there is, in particular, the need for products having improved color and odor quality and a more advantageous low-temperature behavior. Added to this is the fact that in recent years consumer behavior has changed to the effect that consumers place very great value on purely vegetable products. The known vegetable fatty alcohols have iodine numbers in the range below 20 or very high iodine numbers above 100. Fatty alcohols having iodine numbers in the abovementioned range between 20 and 95, which is particularly preferred with regard to application technology, are not known. The blending of fatty alcohols having very different iodine numbers does not lead to satisfactory products. German Laid-open Specification DE-A1 4335781 (Henkel) discloses a process in which the triglycerides present in the vegetable fats or raw materials are firstly cleaved by pressurized cleavage into glycerol and fatty acids, and the latter are esterified with methanol, or the starting materials are directly transesterified to give the fatty acid methyl esters and then the esters are hydrogenated to give the alcohols, either the fatty acid methyl esters or the hydrogenation products being fractionated by removal of an amount of forerunnings such that the end product has an iodine number of from 20 to 110 and a conjuene content of less than 4.5% by weight. Whilst the process can be used for vegetable raw materials such as palm oil for the preparation of unsaturated fatty alcohols in the iodine number range 50 to 65 without problems, if palm oil is used to produce unsaturated fatty alcohols in the iodine number range from 65 to 85, results are obtained which are surprisingly not entirely satisfactory.
The object of the present invention was consequently to provide unsaturated fatty alcohols based on palm oil which have iodine numbers in the range from 65 to 85 and, compared with animal-based unsaturated fatty alcohols, have greater oxidation stability and comparable or better low-temperature behavior. The aim was also to obtain extremely pure coupled products.